Transfer elements and process for preparing same

ABSTRACT

A PRESSURE-SENSITIVE TRANSFER SHEET OR RIBBON COMPRISING A POROUS FABRIC HAVING ON THE SURFACE THEREOF A SPONGE LAYER OF A FOAMED SYNTHETIC THERMOPLASTIC RESIN, SAID FABRIC CONTAINING A SUPPLY OF PRESSURE-TRANSFERABLY INK. IN USE, THE INK IS EXUDED THROUGH THE SPONGE LAYER, WHICH IS PRESENT AT THE INK-RELEASING SURFACE, SO THAT THE PATTERN OF THE FILAMENTS OF THE FABRIC IS NOT TRANSMITTED TO THE FORMED IMAGES.

June 13, 1972 D. A. NEWMAN ETAL. 3,669,713

TRANSFER ELEMENTS AND PROCESS FOR PREPARING SAME Filed Dec. 31, 1969 e ll o @1 i9i f5 /J/ #M /S INVENTORS Dogfa A. New/77m www@ United StatesPatent liice 3,669,713 Patented .lume -13, 1972 8 Claims ABSTRACT 0F THEDISCLOSURE A pressure-sensitive transfer sheet or ribbon kcomprising aporous fabric having on the surface thereof a sponge layer of a foamedsynthetic thermoplastic re'sin, said fabric containing a supply ofpressure-transferable ink. In use, the ink is exuded through the spongelayer, which is present at the ink-releasing surface, so that thepattern of the filaments of the fabric is not transmitted to Vthe formedimages.

This application is a continuation-in-part of parent application Ser.No. 738,496, filed June 20, 1968, now abandoned.

The present invention is concerned with the production of fabricduplicating sheets and ribbons of all types and widths but mostparticularly with typewriter ribbons and printing machine ribbons. Theformer generally are less than 1 inch in width while the latter rangefrom 2 to 16 or more inches in width. Fabric ribbons are most comnronlywoven from threads of filaments of synthetic thermoplastic resin and/ ornatural origin but some non` woven fabrics of such materials are alsoused in which the filaments and/ or threads are matted or randomlyintertwined to form fabrics. Such fabric ribbons, whetherl woven ornon-woven, are impregnated with a pressuretransferable liquid ink andfunction by exuding a portion of such ink to a copy sheet under theimpact of a type face or printing head to form images on the copy sheetcorresponding to the raised image on the impact element.

In order to provide duplicating ribbons which produce sharper copies,such ribbons have been reduced in caliper as much as possible. Thinribbons conform to the raised image outline on the impact device underimpact pressure so that the portion of the ribbon which contacts thecopy sheet is as small as possible. 'Ihus the formed images sharplycorrespond to the raised image outline and are relatively free ofblurred and filled-in areas.

In satisfying these requirements, it has been found that the structureof the ink-containing fabric represents a disadvantage, particularly inthe case of woven fabrics. The images produced exhibit a fabric weaveimprint which represents a loss in the tone or density of the images.This is caused by the fact that the filaments, particularly those ofsynthetic origin, do not absorb ink but merely retain it on theirsurfaces and in pockets or voids between filaments and threads offilaments. Under the effects of impact pressure, the ribbon makesintimate contact lwith the copy sheet. Some of the filaments which arepresent at the surface of the ribbon make intimate contact with the copysheet to form portions of each typed image, while other portions of eachtyped image are formed by contact of the copy sheet with ink-containingpockets or voids between filaments and/or threads. The cause and effectis analogous to the fingerprinting operation. The end result isdisadvantageous since it is desirable to produce typed images which havea uniform intense ink density.

The principal object of the present invention is to provide fabricduplicating 'sheets and ribbons which do not produce a fabric weave orfabric pattern in the images produced therewith and which produce imageshaving uniform intense ink density.

Another object of this invention is to provide a transfer element suchas a duplicating ribbon which uniformly meters ink to each copy sheetunder the effect of imaging pressure and thereby prevents splatteringofthe large amount of ink which may be present in the ribbon,particularly during initial uses thereof. l

It is an advantage of this invention that the present l duplicatingribbons contain their supply of duplicating ink internally and aretherefore cleaner to handle and to use than conventional fabric ribbons.

According to thepresent invention, it has been discovered that suchnovel fabric transfer elements may be produced by applying a thin spongelayer of foamed synthetic thermoplastic resin to an ink-absorbent fabricof w'oven or non-woven filaments, and inking the ribbon in conventionalmanner.

The accompanying drawing illustrates the novel elements of the presentinvention and a continuous process by which they can be produced. In thedrawing:

FIG. l is a sectional vieW of a continuous process for producing thepresent transfer elements, and

FIGS. 2 and 3 are diagrammatic cross-sections, to an enlarged scale, oftransfer elements produced according to two embodiments of the presentinvention.

The preferred methods of applying the 'sponge layer to the fabricsubstrate are (a) by applying a thin layer 15 of a pore-forming resincomposition, such as a mixture of a polyisocyanate and a polyhydricmaterial such as polyester and/or a polyglycol, to one surface of aconventional woven or non-woven ribbon fabric 10 and applying heat toreact and foam the layer in conventional manner, or (b) by forming athin layer of a pore-forming resin composition and thereafter laminatingit to one surface of a conventional woven or non-Woven ribbon fabric.The sponge layer may be laminated to the fabric substrate using anadhesive or solvent-bonding or heatbonding techniques which do notresult in an ink-impervious barrier between the fabric and the spongelayer.

The present invention applies to the production of duplicating fabricsbased upon filaments and/or threads of filaments of synthetic and/ornatural origin. The most common filaments are silk and cotton and thosesynthetic thermoplastic filaments formed of nylon polyamide,polyacrylonitrile (Registered Trademark Orlon), polyester fiber(Registered Trademark Daeron) and cellulose acetate rayon, but othersynthetic fiber-forming materials are also used including polyvinylidenechloride, polycarbonate and the like. Woven ribbons are most commonlyproduced by winding a number of fine filaments together to form threadsand then weaving the threads to form the fabric. Non-woven fabrics aregenerally produced by compacting a number of randomly dispersedfilaments or threads to form a matted fabric of the desired density andcaliper. Thermoplastic resin particles are often incorporated and thefabric is heated to cause the powder to melt and adhere contactingfilaments to each other. The production of such ink-absorbent fabrics iswell-known in the art and forms no part of the present invention.

As illustrated by FIG. l, the uninked fabric 10 may be treated in acontinuous process according to one embodiment of the present invention.The fabric is expended vat 14 containing such solution. The fabriccarryingv coating 1S is passed through a heating tunnel 16 where it iscontacted with hot air to activate the blowing reaction and dry thecoating to form the sponge layer 17. The fabric is then passed overidler roller 18 and compressed between inking rollers 19, each of whichreceives a constant supply of non-drying liquid ink 21v from vats 21a bymeans of application rollers 20. -The inkedfabric`22 is conducted underidler roller 23 and onto take-up roll 24 for subsequent processing. Ifdesired, ink may beapplied to only the fabric side and not to the spongeside.

The duplicating element produced in-this manner has the structureillustrated lby FIG. 2 or FIG. 3 depending upon the structure of thefabric support. In cases where the fabric support is a dense fabric suchas a conventional Woven or non-woven typewriter ribbon fabric, theapplied foam-*forming composition is retained primarilyat and near thesurface of the fabric to which it is applied. The fabric is relativelyimpermeable to the foam-forming composition because of the density ofthe former and the viscosity of the latter, and the duplicating elementproduced has a structure as illustrated by FIG. 2 of the drawing whichshows the element 25 having a fabric support 26 and the sponge layer 27.The fabric support contains a supply of pressure-transferable ink. Thesponge layer may be free of ink, where the fabric is inked separatelyfrom the sponge layer, or may contain ink. However the sponge layerpreferably contains little or no ink and its empty pores function tometer ink from the fabric to a copy sheet. The inking procedure of FIG.l in which the element is compressed during inking causes most of theink to be taken up by the fabric whereas the sponge layer absorbs airfrom the atmosphere when the compression is relaxed.

In cases where the fabric support is a loosely woven or non-wovenfabric, such as cheesecloth, which consists of a very open, porousstructure, the applied foam-forming composition permeates the fabricsince the composition is able to flow through the fabric. The fabric isthus embedded in the foam-forming composition and the expansion of thecomposition during foaming insures that a porous sponge surface isformed at both surfaces of the fabric. Ribbons produced in this mannerare illustrated by FIG. 3 of the drawing which shows the ribbon 28having a fabric support 29 embedded within the sponge layer 30, all ofwhich contain a supply of pressure-transferable ink.

If desired, the ribbons produced according to this embodiment may havethe sponge layer 30 present at only the ink-releasing surface of thefabric support 29 as well as impregnated therein. This is accomplishedby applying the foam-forming composition to the open fabric while thefabric is held closely against an impermeable casting support such as ametal roller or ilat glass surface, and then foaming the compositionwhile the fabric is m-aintained against the support. The compositionpermeates the fabric and expands towards the free surface. An advantageof this procedure is that the foam-forming composition develops arelatively ink-impermeablesurface adjacent the casting support so thatthe formed ribbon transfers only minor amounts of ink back to the typeface whereby nearly the entire ink supply is preserved for transferthrough the sponge layer 30 to the sheets being imaged.

The present sponge layer contains an open, interconnected cell structureand may be applied according to any of the well-known processes andusing any of the wellknown foam-forming compositions based on asynthetic thermoplastic binder material. The most common foamformingcompositions are those which produce foamed polyurethane layers of theopen-celled or reticulated types.

4 These are based upon compositions containing a diisocyanate, acompound containing reactive hydrogen, water and a catalyst. Thereactive hydrogen compound is a difunctional polyester such as an adipicacid-ethylene glycol reaction product of about 2000 molecular weight, ora difunctional polyether condensate containing hydroxyl groups, or adifunctional polyamine. The reaction proceeds rapidly and liberatescarbon dioxide which causes the foaming action.L Reference is made toU.S. Pats. Nos. 2,900,278; 3,171,820 and 3,382,090 for their disclosureof materials and processes for producing polyurethane layers of therequired types.

If desired, other synthetic thermoplastic resin systems may be usedincluding the foam-forming rubbers such as chloroprene andbutadiene-styrene and the pore-forming vinyl resins such as vinylchloride, methyl methacrylate, acrylonitrile, styrene and copolymersthereof. Such resins require the presence of a small amount of aconventional gas-liberating or blowing agent which is heat-activated toproduce the desired open, interconnected pores. Agents such asdi-N-nitroso pentamethylene tetramine, di-N- nitroso piperazine and p,poxybis (benzenesulfonyl hydrazide) are suitable.

The foam-forming -composition is applied to one or both sides of thefabric 10 in the form of a very thin continuous coating 15 according toone embodiment. The idea is to apply the thinnest possible layer whichproduces a uniform continuous covering of the fabric surface, leavingthe body of the fabric impregnated, with the composition or free of thecomposition, as desired. Amounts ranging from about 0.05 pound up toabout 1 pound per ream of fabric are suitable, a ream being equal to3300 square feet of fabric surface. The coated fabric is then heated tothe required temperature fora sufficient period vof time to causepolymerization of the foam-form ing composition and/or activation of theblowing agent. This results in an increase in the thickness of theportion of the sponge layer present on the fabric surface to the pointthat it has a measurable caliper which is preferably no greater thanabout one-sixteenth of an inch.

, The foam layer 17 produced has an open, interconnected cell structurewhich permits free circulation of the ink and free transfer of the inkto the copy sheet without period of time to cause polymerization of thefoam-formundue filtering of the pigment of the ink from its oilyvehicle. In this connection it is pointed out that the pigment of theink has a particle size of about 5 microns so that the foam layer mustcontain cells having a size greater than 5 microns. The cell size shouldrange between 6 and 50 microns and preferably is within the range ofabout 10 to 30 microns.

At this stage the foam-coated fabric is ready for inking. The inkcomprises a conventional,oil-and-pigment ink such as a mixture of oleicacid, carbon black and nigrosine black. As indicated supra, the pigmentmust have a particle size smaller than the cell sizeof the sponge layer.The ink 21 may be applied to both sides of the fabric as` shown in FIG.1 or, if desired, may be applied only to one side. A greater amount ofink can be applied to the ribbon because of the presence of the spongelayer 17 and also because the sponge layer 17 prevents the ink fromsplattering on the copy sheet during use. This unexpected advantageappears to be due to the open, interconnected cell structure whereby thesponge layer retains the liquid ink uniformly dispersed in the interiorthereof, apparently by capillary action. There are "no surface pools orreservoirs of ink at the foam surface The uninked fabric is teratedaccording to the method of FIG. l. The foam-forming composition presentin vat 14 is as follows:

The foam-forming composition is a milky liquid which is printed onto thefabric as a thin, continuous layer 15 which completely wets and coversthe fabric surface. The layer is applied at a weight of about 0.25lb./ream and may be spread and levelled after printing by means of adoctor blade, if desired. The coated web is then passed through a dryingtunnel containing a continuous supply of forced hot air. The temperaturewithin the tunnel is about 150 C. and the foaming action occurs nearlyinstantaneously as the ingredients react and liberate carbon dioxide gaswhich produces the reticulated cellular structure within thepolyurethane resin formed. The porous layer 17 comprises a microspongeof polyurethane containing empty micropores which are interconnected andwhich are sufficiently large as to transmit pigment particles of lessthan 10 micron size.

Next the coated fabric is passed in the nip of inking rollers 19 whichapply ink received from vats 21a by means of application rollers 20. Theink may be a conventional ink comprising oleic acid as the oily vehicleand carbon black and nigrosine black colorants. The ink is initiallyground in a ball mill so that the pigment particles are very fine andpreferably average about 5 microns in diameter. If desired, the ribbonink may contain dissolved dyestuff in place of solid pigment, suchpigment-free ribbon inks being well-known in the art.

Finally the inked fabric is wound on take-up roll 24 for aging andsubsequent processing. The inked web may be slit into ribbons of thedesired width by means of heated cutter blades which fuse the cut edges.

As indicated hereinbefore, the composition of the sponge layer 15 andthe method by which it is applied to the fabric support 10 are notcritical so long as the layer 17 is an open sponge which will transmitthe ribbon ink from the ribbon to a copy sheet under imaging pressure.Nearly any open sponge layer will accomplish this result unlesspreventive steps are taken to regulate the pore size to a smaller rangeand unless an impervious barrier is applied or formed between the fabricand the sponge.

.In cases where the sponge layer 27 is produced separately from thefabric 26 and thereafter laminated thereto, caution must be taken toavoid the formation of a barrier. This may be accomplished Iby wettingthe surface of the fabric with a small amount of a volatile liquid whichis a solvent for the sponge and a non-solvent for the fabric. Thesurfaces are brought together and heat is applied to evaporate thesolvent. Alternatively controlled heating may be used, or a small amountof a very dilute solution of an adhesive resin binder may be applied tothe fabric surface to coat only the exposed :fibers at the fabricsurface, and the ribbon is dried immediately after the sponge layer iscontacted therewith to form a discontinuous adhesive bond between thefabric and the sponge layer.

In cases where the foam-forming composition is one which is unstable atroom temperature, it is preferred to apply the composition to the fabricas separate stable coreactants, which are thereafter spread together ina thin layer and reacted. Such procedures are well known in the art offorming sponge layers.

It should be understood that it is also possible to apply the spongelayer 27 to the fabric 26 after the fabric has been inked. An inlk-freesponge layer is cleaner to the touch and thus is advantageous where thelife span of the ribbon is of less importance than cleanliness. We havefound that the foam-forming compositions have sufficient afiinity forthe surface of an inked fabric to remain bonded thereto during use, andalso that a preformed sponge layer can be bonded to the surface of aninked fabric by the techniques listed hereinbefore. Ribbons ac coring tothis embodiment also produce images which are free of fabric weavepatterns and which have good uniform tone density due to the fact thatthe sponge layer 27 compresses under impact and permits the ink 21 fromthe fabric 26 to pass through to the copy sheet.

It is also possible to produce the present transfer elements by cuttingthe fabric web 10 into desired widths and thereafter applying the spongelayer 17 and impregnating the elements with ink 21. However it ispreferable to process the fabric in web form and thereafter cut thecoated and inked web into ribbons or sheets of the desired width.

Variations and modifications may tbe made within the scope of the claimsand portions of the improvements may be used without others.

We claim:

1. The process of producing a pressure-sensitive inkreleasingduplicating element which comprises the steps of:

(a) providing a thin ink-absorbent fabric of filaments;

(b) bonding to at least one surface of said fabric a thin syntheticthermoplastic sponge layer containing gas-filled, ink-transmissivepores; and thereafter (c) impregnating said fabric with a non-dryingliquid ink to form a duplicating element which is capable of uniformlymetering said ink from said fabric through said sponge layer to formimages on a copy `sheet under the effects of imaging pressure withoutsplattering of the ink and Without forming a fabric imprint in saidimages.

2. The process of claim 1 in which the sponge layer is formed on thefabric by applying thereto a continuous coating comprising a syntheticthermoplastic resin-forming composition which is heat-reactive toliberate a gas, and heating said coating to liberate said gas and formsaid thin sponge layer.

3. The process of claim 2 in which the resin-forming compositioncomprises a polyurethane resin-forming composition.

4. y'The process of claim 1 in which the sponge layer is preformed andthereafter laminated to the fabric.

5. The process of claim 1 in which the fabric is a conventional Wovennylon fabric.

6. A pressure-sensitive, ink-releasing duplicating element producedaccording to the process of claim 1.

7. A pressure-sensitive, ink-releasing duplicating element producedaccording to the process of claim 3.

8. A pressure-sensitive, ink-releasing duplicating element producedaccording to the process of claim 5.

References Cited UNITED STATES PATENTS 3,104,980 9/ 1963 Maiersonl17-36.4 3,080,954 3/ 1963 Newman et al. 117-36.4 3,442,681 5/1969Newman et al. 117-364 MURRAY KATZ, Primary Examiner U.S. Cl. X.R.

bei

PO-lOb 569 n n U Cssfmiemeof come@ Patent No. 3,669,715 Dated .Tunewrm?? Inventor) Douglas A. Newman and Allan T. Sohlotzhauer v- It iscertified tbat'error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

'- Column L+, line 4L should be deleted it isa repetitien of line 35.

Column 5, line l, .terated" should read treated Signed and sealed thijs26th day of September 1972.

(SEAL) Attest:

ROBERT GOTTSCHALK Commissioner of Patents EDWARD M.FLETCHER,JR.Attesting Officer

